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Back-contamination is the informal but widely employed name for the hypothetical introduction of microbial extraterrestrial organisms into Earth's biosphere. It is assumed that any such contact will be disruptive or at least have consequences over which human beings will have little control. The threat of back-contamination from the Moon was the main reason for quarantine procedures adopted for the Apollo program, up until the completion of Apollo 14. Astronauts and lunar samples were quarantined in the Lunar Receiving Laboratory.

The likelihood that a human being or any other animal could literally acquire an alien virus is effectively nil, as viruses are host specific. This does not mean that extraterrestrial microbes cannot act upon one pathogenically: spores might use an organism's body as hosts, while the ingestion of bacteria in any form could produce toxic chemicals. When human beings ingest contaminated food, for example, they are not acquiring a virus in the manner of the flu but the experience may still be lethal because of toxic compounds.

Further, the possibility exists that a microbe might aggressively metabolize some Earth resource were it introduced here, altering atmospheric conditions or the water cycle.

Back contamination from Mars

Since the Moon is now generally considered to be free from life, the most likely source of contamination is Mars. It would arise during a Mars sample return.

Since it is currently unknown whether or not life forms exist on Mars, the mission could potentially transfer viable organisms resulting in back contamination — the introduction of extraterrestrial organisms into Earth's biosphere. The mainstream scientific view as expressed by the NRC and ESF studies and the Office of Planetary Protection is that the risk of harmful back contamination is probably very low, but cannot be demonstrated to be zero. In the worst case scenario (thought to be very low probability) this could lead to environmental disruption and impact on countries outside the nation responsible for the mission. As a result, returned samples from Mars will be treated as potentially biohazardous until scientists can determine that they are safe.

The sample return mission will be designed to break the chain of contact between Mars and the exterior of the sample container, for instance, by sealing the returned container inside another larger container in the vacuum of space before return to Earth. In order to eliminate the risk of parachute failure, the current plan is to return the capsule to the Earth without the use of parachutes: the capsule will fall at terminal velocity and the impact will be cushioned by the capsule's thermal protection system. The sample container will be designed to withstand the force of the impact.

To receive the returned samples, NASA has proposed to build a biohazard containment facility - known as the Mars Sample Return Receiving facility (MSRRF).

The proposed sample return facility must be a biohazard level 4 laboratory. However, it must also contain unknown biohazards and the sizes of any putative Martian micro-organisms are unknown. In consideration of this, the ESF proposed additional requirements. Ideally it should contain particles of 0.01 µm, or larger, and release of a particle 0.05 µm or larger is unacceptable under any circumstances. It also must double as a clean room to preserve the science value of the samples. A clean room is normally kept at a higher pressure than the external environmnent to keep contaminants out, and a biohazrad laboratory is kept at a lower pressure to keep the biohazards in. This introduces conflicting requirements and requires a novel architecture that will take some years from design to completion. Preliminary studies have warned that it may take as many as 7 to 10 years to get it operational and an additional two years is recommended for the staff to become accustomed to the facilities.

Legal requirements and need for public debate

The ESF report also considered the legal situation. In the event of a release of the contents of the MSR capsule during return to Earth then the state responsible has liability in respect to any damages caused under the Outer Space Treaty. This liability is unlimited in either amount or in time. The situation as regards liability is less clear if the release occurs after return to Earth.

The proposed NASA Mars Sample Return mission will not be approved by NASA until the National Environmental Policy Act (NEPA) process has been completed. The NEPA process would require a public review of all potential impacts that could result from MSR, including worst case back contamination scenarios. It is likely that a formal Environmental Impact Statement (EIS) would have to be prepared. The quarantine situation would also need to be clarified. There are also numerous international regulations and treaties to be negotiated in the case of a Mars Sample Return, especially those relating to environmental protection and health.

The ESF report ends with a series of recommendations. On the need for public debate they say

RECOMMENDATION 10: Considering the global nature of the issue, consequences resulting from an unintended release could be borne by a larger set of countries than those involved in the programme. It is recommended that mechanisms dedicated to ethical and social issues of the risks and benefits raised by an MSR are set up at the international level and are open to representatives of all countries

Several other papers and studies have come to the same conclusion.

Differing views on a MSR

Carl Sagan was first to raise back contamination concerns. In Cosmic Connection (1973) he writes:

Precisely because Mars is an environment of great potential biological interest, it is possible that on Mars there are pathogens, organisms which, if transported to the terrestrial environment, might do enormous biological damage.

This possibility has been confirmed in all the later studies, as the worst case scenario. It is considered low probability but can't be ruled out.

Later in Cosmos (1980) he wrote

Perhaps Martian samples can be safely returned to Earth. But I would want to be very sure before considering a returned-sample mission.

The PPO and NASA and ESA view is that with present day technology, Martian samples can be safely returned to Earth provided the right precautions are taken.

There are dissenting views however.

The International Committee Against Mars Sample Return maintains that it is not possible to return samples to Earth safely at this stage. They urge more in situ studies on Mars first, and preliminary biohazard testing in space before the samples are returned to Earth.

At the other extreme, Robert Zubrin (Mars surface colonization advocate and director of the Mars Society) maintains that the risk of back contamination has no scientific validity.

See also

• Aerobiology
• Astrobiology
• Extraterrestrial life
• Forward-contamination
• Living Interplanetary Flight Experiment
• Manned mission to Mars
• Panspermia
• Planetary protection
• Red rain in Kerala

References

1. The risks of environmental disruption resulting from the inadvertent contamination of Earth with putative martian microbes are still considered to be low. But since the risk cannot be demonstrated to be zero, due care and caution must be exercised in handling any martian materials returned to Earth. Assessment of Planetary Protection Requirements for Mars Sample Return Missions (Report). National Research Council. 2009.

2. ^ European Science Foundation - Mars Sample Return backward contamination - Strategic advice and requirements July, 2012, ISBN 978-2-918428-67-1 - see Back Planetary Protection section. (for more details of the document see abstract )
3. Joshua Lederberg Parasites Face a Perpetual Dilemma Volume 65, Number 2, 1999 / American Society for Microbiology News 77.
4. Assessment of Planetary Protection Requirements for Mars Sample Return Missions (Report). National Research Council. 2009. {{cite report}}: Cite has empty unknown parameter: |1= (help)
5. http://mepag.nasa.gov/reports/iMARS_FinalReport.pdf Preliminary Planning for an International Mars Sample Return Mission Report of the International Mars Architecture for the Return of Samples (iMARS) Working Group June 1, 2008
6. http://planetaryprotection.nasa.gov/summary/msr Mars Sample Return: Issues and Recommendations. Task Group on Issues in Sample Return. National Academies Press, Washington, DC (1997).
7. ^ http://mepag.jpl.nasa.gov/meeting/mar-10/Li2-MSR_Dis-for-MEPAG3-17_tech_updates.pdf Mars Sample Return Discussions As presented on February 23, 2010
8. Mars Sample Return Receiving Facility
9. Mars Sample Return Receiving Facility - A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth (PDF) (Report). 2002. A Sample Return Facility will require combining technologies used for constructing maximum containment laboratories (e.g. Biosafety Level 4 labs), which will be needed to ensure protection of Earth from the Mars samples, with cleanroom technologies, which will be needed to protect the Mars samples from Earth contamination.
   
   • Such an integrated facility is not currently available.
   
   Planetary Protection Requires Negative Air Flow to Protect Against Environmental Contamination Planetary Science and Planetary Protection Require Positive Air Flow to Protect Samples from Terrestrial Contamination {{cite report}}: line feed character in |title= at position 19 (help)
10. A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth
11. [http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1395.pdf CLEANROOM ROBOTICS – APPROPRIATE TECHNOLOGY FOR A SAMPLE RECEIVING FACILITY ? 2005 update on the Draft Test Protocol ].
12. 2010 Mars Sample Return Orbiter decadal survey:

    The NASA Planetary Protection Officer commissioned the development of a draft test protocol that would represent one “necessary and sufficient” approach to evaluate the safety of the samples while safeguarding the purity of the samples from terrestrial contamination. A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth was published in October 2002 . In 2003, three architectural design teams independently examined the scope, approach, cost, and technology required for the SRF, using the Draft Test Protocol for requirements. The approaches varied from allrobotic handling of samples to more traditional glove box implementations. The studies indicated that the principles and techniques required are generally mature. Biosafety laboratories, the NASA Lunar Sample Facility, pharmaceutical laboratories, and electronic fabrication cleanrooms perform most of the required individual functions. However, there are some areas needing early development, such as ensuring sample preservation and bio-safety together, representing new challenges that were addressed by techniques like dual-walled containers (and gloves) with positive pressure clean inert gas in between the walls. This, as well as some further development in ultra-clean sample manipulation, safe and pure transport of samples, and sample sterilization techniques, are planned in the technology program

13. "7: "Sample-Receiving Facility and Program Oversight"". Assessment of Planetary Protection Requirements for Mars Sample Return Missions (Report). National Research Council. 2009. p. 59. It has been estimated that the planning, design, site selection, environmental reviews, approvals, construction, commissioning, and pre-testing of a proposed SRF will occur 7 to 10 years before actual operations begin. In addition, 5 to 6 years will likely be required for refinement and maturation of SRF-associated technologies for safely containing and handling samples to avoid contamination and to further develop and refine biohazard-test protocols. Many of the capabilities and technologies will either be entirely new or will be required to meet the unusual challenges of integration into an overall (end-to-end) Mars sample return program. {{cite report}}: Unknown parameter |http://www.nap.edu/openbook.php?record_id= ignored (help)
14. Mars Sample Return: Issues and Recommendations (Planetary Protection Office Summary) Task Group on Issues in Sample Return. National Academies Press, Washington, DC (1997)
15. "7: "Sample-Receiving Facility and Program Oversight"". Assessment of Planetary Protection Requirements for Mars Sample Return Missions (Report). National Research Council. 2009. p. 59. It has been estimated that the planning, design, site selection, environmental reviews, approvals, construction, commissioning, and pre-testing of a proposed SRF will occur 7 to 10 years before actual operations begin.17,18,19 In addition, 5 to 6 years will likely be required for refinement and maturation of SRF-associated technologies for safely containing and handling samples to avoid contamination and to further develop and refine biohazard-test protocols. Many of the capabilities and technologies will either be entirely new or will be required to meet the unusual challenges of integration into an overall (end-to-end) Mars sample return program. {{cite report}}: Unknown parameter |http://www.nap.edu/openbook.php?record_id= ignored (help)
16. M. S. Race Planetary Protection, Legal Ambiguity, and the Decision Making Process for Mars Sample Return, Adv. Space Res. vol 18 no 1/2 pp (1/2)345-(1/2)350 1996
17. Carl Sagan,The Cosmic Connection - an Extraterrestrial Perspective (1973) ISBN 0521783038
18. Carl Sagan Cosmos Random House Publishing Group, 6 Jul 2011
19. International Committee Against Mars Sample Return
20. Robert Zubrin "Contamination From Mars: No Threat", The Planetary Report July/Aug. 2000, P.4–5
21. transcription of a tele-conference interview with ROBERT ZUBRIN conducted on March 30, 2001 by the class members of STS497 I, "Space Colonization"; Instructor: Dr. Chris Churchill

External links

• NASA page on back-contamination

• Articles to be merged from June 2013
• Astrobiology
• Extraterrestrial life